The present invention generally relates to a dielectric filter which has a plurality of dielectric resonators of a TM.sub.010 mode or its modified mode.
Conventionally, in this type of dielectric filter, as shown in FIG. 16, a cavity case 54 is made entirely of ceramics, having a linear-expansion coefficient which is the same or substantially the same as that of the dielectric poles 52, the cavity case being accommodated within a metallic case (not shown). This prevents any deterioration of the temperature response characteristics through the combination of the ceramic cavity case 54 and the ceramic dielectric poles 52, since these have the same linear-expansion coefficient. The cavity case 54 has partitions 54a for adjusting the electro-magnetic coupling between the resonators and conductive films 56 for forming actual current paths thereon. If the cavity case were made of metal and the dielectric poles 52 were soldered to it, in addition to adversely affecting the temperature response characterstics, the Q of the resonator would be considerably lowered because of Joule loss in the solder portion.
However, in the conventional dielectric filter of FIG. 16, such a cavity case 54, as described hereinabove, which is entirely made of ceramics and has several stages of dielectric resonators, is required to have a size corresponding to the number of the stages of the resonators, with chambers being provided, made of ceramic plate. Therefore, as the case becomes larger, the assembling operation becomes more complex, and the assembling thereof becomes harder to perform. Also, larger ceramic plates are required to make the cavity case, and the material becomes more expensive, thus resulting in higher cost.